Generally, the process of electrostatographic copying is initiated by exposing a light image of an original document to a substantially uniformly charged photoreceptive member. Exposing the charged photoreceptive member to a light image discharges its surface in areas which correspond to non-image areas in the original document while maintaining the charge in image areas. This selective discharging scheme results in the creation of an electrostatic latent image of the original document on the surface of the photoreceptive member. This latent image is developed into a visible image by a process in which developer material is deposited onto the surface of the photoreceptive member. Typically, this developer material comprises carrier granules having toner particles adhering triboelectrically thereto, wherein the toner particles are electrostatically attracted from the carrier granules to the latent image for forming a powder toner image on the photoreceptive member. Alternatively, liquid developer materials comprising a liquid carrier material having toner particles dispersed therein have been utilized. In a liquid developing process, the developer material is applied to the latent image with the toner particles being attracted toward the image areas to form a liquid image. Regardless of the type of developer material employed, the toner particles of the developed image are subsequently transferred from the photoreceptive member to a copy sheet, either directly or by way of an intermediate transfer member. Once on the copy sheet, the image may be permanently affixed to provide a "hard copy" reproduction of the original document or file. The photoreceptive member is then cleaned to remove any charge and/or residual developing material from its surface in preparation for subsequent imaging cycles.
The above described electrostatographic reproduction process is well known and is useful for light lens copying from an original, as well as for printing applications involving electronically generated or stored originals. Analogous processes also exist in other printing applications such as, for example, digital laser printing where a latent image is formed on the photoconductive surface via a modulated laser beam, or ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images. Some of these printing processes develop toner on the discharged area, known as DAD, or "write black" systems, in contradistinction to the light lens generated image systems which develop toner on the charged areas, knows as CAD, or "write white" systems. The subject invention applies to both such systems.
The use of liquid developer materials in imaging processes and the art of developing electrostatographic latent images formed on a photoconductive surface with liquid developer materials are well known. Indeed, various types of liquid developing systems have heretofore been disclosed. Liquid developers have many advantages, and often produce images of higher quality than those formed using dry toners. For example, images developed with liquid developers can be made to adhere to paper without a fixing or fusing step, thereby eliminating a requirement to include a resin in the liquid developer for fusing purposes. In addition, the toner particles can be made to be very small without resulting in problems often associated with small particle powder toners, such as airborne contamination which can adversely affect machine reliability and can create potential health hazards. Development with liquid developers in full color imaging processes also has many advantages, including, among others, production of a texturally attractive output document due to minimal multi-layer toner height build-up (whereas full color images developed with dry toners often exhibit substantial height build-up of the image in regions where color areas overlap). In addition, full color imaging with liquid developers is economically attractive, particularly if surplus liquid carrier containing the toner particles can be economically recovered without cross contamination of colorants. Further, full color prints made with liquid developers can be processed to a substantially uniform finish, whereas uniformity of finish is difficult to achieve with powder toners due to a need for thermal fusion, in addition to variations in the toner pile height and other factors.
When using liquid toners, there is a need to remove the liquid carrier medium from the photoconductive surface after the toner has been applied thereto. This prevents the liquid carrier from being transferred from the photoreceptor to the paper or to the intermediate medium during image transfer. Removing the liquid carrier also allows it to be recovered for recycle and reuse in the developer system. This provides for additional cost savings in terms of printing supplies, and helps eliminate environmental and health concerns which result from disposal of excess liquid carrier medium. Furthermore, removing the liquid carrier increases the mechanical strength of the image which prevents it from being damaged during subsequent processing steps.
One way to remove excess carrier fluid is to place a blotting member in rotatable contact with the image while it resides on the photoreceptor or intermediate imaging member. A vacuum associated with the blotting member causes the liquid to be pulled from the photoreceptor surface. Removal of carrier fluid results in an increase in solid particle content, thereby allowing for greater efficiency of the process of transferring the image from the imaging member to permanent media. The most efficient conditioning of an image to increase the percentage of solids residing therein obviously requires preventing the solid toner particles from leaving the image while the carrier liquid is being removed. This process must be completed without disturbing the toner image.
Typical methods of removing excess fluid using a blotting member require passing the imaging member directly under the roll to absorb the contacting liquid carrier fluid. The strength of the vacuum associated with the roll is determined by the speed at which the imaging member moves past the roll. Specifically, faster process speeds require a higher vacuum to be applied to the image in order to remove a sufficient amount of fluid. Vacuum systems that are capable of supplying a sufficient amount of suction are often quite large and take up too much space within the printing machine. In addition, significant costs can be associated with purchasing and operating a high capacity vacuum system. Thus, it is advantageous to devise a system which can remove excess carrier fluid from the surface of an imaging member without requiring the application of a high vacuum.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,332,642 to Simms et al. Issued Jul. 26, 1994 discloses a device for increasing the solids content of an image formed from liquid developer wherein absorption material is contacted with a liquid carrier laden image and the absorbed liquid carrier is vacuumed out of the absorption material. The absorption material preferably is a conductive cover on a porous roller biased with an electrical charge which is the same as the charge of the toner particles.
U.S. Pat. No. 5,352,558 to Simms et al. issued Oct. 4, 1994 discloses a device for increasing the solids content of an image formed from liquid developer which includes an absorption material containing small pores to absorb dispersant from a dispersant laden image and a pair of rollers bearing the belt. The belt on one of the rollers contacts a dispersant laden image bearing portion of an image carrying member such as a photoreceptor drum or an intermediate sheet
U.S. Pat. No. 5,047,808 to Landa et. al issued Sep. 10, 1991 discloses an image system including an image bearing surface and an intermediate transfer member operative for transfer of liquid toner images from the image bearing surface to a substrate. The system provides for first transfer engagement between the intermediate transfer member and the image bearing surface for transfer of an image from the image bearing surface to the intermediate transfer member at a first pressure, and then provides for second transfer engagement between the intermediate transfer member and the substrate for transfer of the image from the intermediate transfer member to the substrate at a second pressure. Application of the first pressure produces deformation of the intermediate transfer member to a first deformation degree, while the second pressure application produces deformation of the intermediate transfer member to a second deformation degree.
All of the references cited herein are incorporated by reference for their teachings.
Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for method and apparatus for reproducing images that have been developed using a liquid developer material.
Further, there is a need for methods and apparatus for removing excess carrier fluid from the surface of a liquid developed image, to allow for a more efficient system of reproducing these types of images.